BN44-00195A strikes back!

[steven10]

Re: BN44-00195A strikes back!

Hi, I had the same problem, while using my pc i heard a pop...
black screen and solid blue led...

I found that the 0.22 ohm fuse resistor was blown and the
two mosfets are shorted(FQPF9N50C).
I removed these components and then found that two pins of the TM802(EE1312?) are no longer shorted, compared to the identical ones in the opposite side.
all the other components seems to be fine.
is this normal? should i replace this transfomer?
Thank you all in advance.

[budm]

Re: BN44-00195A strikes back!

"Just a not-so-important question: for some reason, now the blue standby led of the monitor is a lot dimmer than before" That LED runs off the either 5V or 3.3V drive circuits, so as long as your power supply is putting out the correct Voltages, then you will have to look at the LED driver circuits to see why it is dim by checking the DCV feeding the main board.

"Namely, the fusible resistor with a tolerance of 10%, the 12nF cap @800V instead of 630V, and the 47pf and 2.2nF ceramic caps @2kV instead of 1kV." no affect.

[Galandil]

Re: BN44-00195A strikes back!

Update.

Today I received all the pieces finally, and mounted them. Operation 245B+ successful, now it's working again.

Thanks budm for all the advices.

Just a not-so-important question: for some reason, now the blue standby led of the monitor is a lot dimmer than before. Can it depend on the fact that some pieces are not exactly the same as before?

Namely, the fusible resistor with a tolerance of 10%, the 12nF cap @800V instead of 630V, and the 47pf and 2.2nF ceramic caps @2kV instead of 1kV.

I'm just curious about it, all the other caps/resistors are exactly the same as the ones before.

[Galandil]

Re: BN44-00195A strikes back!

Well thanks for all the help, budm. I'll put the orders and I'll report back as soon I finish getting back (in working state, I hope) the monitor.

[budm]

Re: BN44-00195A strikes back!

The CF has Fast recovery Body diode, the CF should be fine to use.

[Galandil]

Re: BN44-00195A strikes back!

10% or 5% is not critical. That should be fine.

Ok, thanks, just one last thing: I just want to be sure and buy the 2 MOSFETs as a replacement in case something goes wrong or they'll break in the future.

The code is FQPF9N50C, and I can see that this product is discontinued by Fairchild, now they sell the FQPF9N50CF. Is it ok in case to use the new one?

The specs are these:

C - https://cdn.badcaps-static.com/pdfs/...73d52af526.pdf
CF - https://cdn.badcaps-static.com/pdfs/...9d1150d5cf.pdf

[budm]

Re: BN44-00195A strikes back!

10% or 5% is not critical. That should be fine.

[Galandil]

Re: BN44-00195A strikes back!

Ok, I managed to find a shop that sells all the capacitors I need (including the ceramic ones and the 12nF 800V).

Now, I'm almost done with the pieces needed, except for one: the dreaded R22 1W 5% fusible resistor. Apparently, it's almost impossible to find one such resistor, in all italian online big shops I couldn't find it, Mouser doesn't have it, Digikey doesn't display the price since it's a non-stock (and apparently you need to order a large quantity, 2000 pieces), etc.

The only available resistor that I found available on an online shop is this:
The only difference is the tolerance, 10% instead of 5%.

Can I go with it the same?

[budm]

Re: BN44-00195A strikes back!

You can try replacing the damaged parts first and see if you do have 24VDC or not, if not then that 12nF will have to be tested for capacitance some how.

[Galandil]

Re: BN44-00195A strikes back!

"How am I supposed to check the capacitance without an ESR tester?" You are testing the capacitance of that cap not ESR.

But my meter doesn't have a capacitance mode.

This is my meter: (and atm I can't even check currents, since I just discovered that the internal fuse is shot damnit).

[budm]

Re: BN44-00195A strikes back!

"How am I supposed to check the capacitance without an ESR tester?" You are testing the capacitance of that cap not ESR.

The MOSFETs when they failed it will show very low resistance between S and D pins so yours are OK then.

[Galandil]

Re: BN44-00195A strikes back!

So the 0.22 Ohms fusible resistor is OK then? I thought you cannot measure it. When those blue disc caps shorted out, they will take out that fusible resistor with it.
The fusible resistor is used for feed the Voltage to run the 24V POWER SUPPLY, the two Power MOSFETs QM802, QM803, and the caps CM802, CM809, CM812 are part of the circuits for driving the transformer TM801S for the 24V.

Ok, this evening I removed the .22 resistor from the board, measured it and... nothing, it's an open circuit so I guess it's blown.

You need to check its capacitance and also check the resistance to see if it has leakage resistance, you need to remove it to do the test.

How am I supposed to check the capacitance without an ESR tester?
I removed the cap and tested for resistance: open circuit always. IIRC caps should show a raising resistance with the tester in ohm measurement mode. Should I try some other test?

You should also check the resistance between Source and Drain pin of Power MOSFETs QM802, QM803 to make sure they do not show low resistance readings, you can test them on board, if they do show low resistance then you need to remove them off the board and test them again.

Don't those 2 MOSFETs have a diode between source and drain? I checked for it with the diode test mode on the meter, and the diode was working good in both FETs, open circuit when inversely polarized, and a drop of .587V for both when directly polarized. Or did you mean some other test?

TY for the patience though, and please remember that I know very little on the topic.

[budm]

Re: BN44-00195A strikes back!

"RM801: from the color, I guess this is a 0.22 ohm 5% (red/red/silver/gold) (I wasn't able to measure it)"
So the 0.22 Ohms fusible resistor is OK then? I thought you cannot measure it. When those blue disc caps shorted out, they will take out that fusible resistor with it.
The fusible resistor is used for feed the Voltage to run the 24V POWER SUPPLY, the two Power MOSFETs QM802, QM803, and the caps CM802, CM809, CM812 are part of the circuits for driving the transformer TM801S for the 24V.

"Now the only problem remains with the 12nF, what happens if it's shot" You need to check its capacitance and also check the resistance to see if it has leakage resistance, you need to remove it to do the test.

You should also check the resistance between Source and Drain pin of Power MOSFETs QM802, QM803 to make sure they do not show low resistance readings, you can test them on board, if they do show low resistance then you need to remove them off the board and test them again.

[Galandil]

Re: BN44-00195A strikes back!

It has to be fusible flame proof type and correct Wattage due to safety requirement. You do want the monitor to catch fire when there is problem.

Then I need to de-solder it in order to check if the actual one is ok. From the photo, it seems that it hasn't blown/taken fire, can you confirm pls?

However, since all the resistors measured ok, I guess I can skip them.

Now the only problem remains with the 12nF, what happens if it's shot and I proceed to mount all the other caps and turn on the power board? Is there any risk that something else will break again, or it will just not function? If it's the latter, I can take the risk and order and mount all the other pieces.

[budm]

Re: BN44-00195A strikes back!

It has to be fusible flame proof type and correct Wattage due to safety requirement. You do want the monitor to catch fire when there is problem.

[Galandil]

Re: BN44-00195A strikes back!

From that shop, there're no MOX 0.22 resistor with 1W, the only one has a power rating of 0.6W.

There's a 0.22 resistor with a power rating of 2.5W though, it's a wirewound resistor, this is the specs sheet:

Which one should I get?

[budm]

Re: BN44-00195A strikes back!

RB801, RB802 = 100K Ohms, 5%, 1W, Flame proof MOX (Metal Oxide).
RB808 = 2 Ohms, 5%, 1W, Flame proof MOX (Metal Oxide).
RB801S = 33 Ohms, 5%, 1W, Flame proof MOX (Metal Oxide).
Per your readings, they are OK.

RM801 = 0.22 Ohms, 5%, 1W, Fusible Resistor Flame proof MOX (Metal Oxide).

Notes: if the resistance tested OK then no need to replace them.

[Galandil]

Re: BN44-00195A strikes back!

Regarding the resistors, I've found these as substitutes (all metal film):

2x100k ohm 1W
33 ohm 1W
2 ohm 0.6W
0.22 ohm 0.6W

Dunno if the power ratings are ok for each resistor, there're even power resistors for the 0.22 one with a power rating of 2.5W.

About checking the 12nF cap, I'd have serious problems in doing that, as I said I don't have an ESR meter, I checked the resistance with the meter set to 2M and the value stopped almost instantly at 206 instead of going up indefinitely. Can it be because I tested the cap on board?

[budm]

Re: BN44-00195A strikes back!

Regarding to the resistor values, I will have to dig up those blown up board to look at them.
The 12nF cap, you can test the capacitance to see if it is still showing the correct capacitance, when this cap goes bad, the capacitance will be way off (less capacitance).

[Galandil]

Re: BN44-00195A strikes back!

Ty for the info about the ceramic caps. I didn't find them on that store, but apparently a guy on ebay from the UK has both of them with a 2kV rating.

Fact is, though, I have serious problems in finding the 12nF 630V (800V) 3% cap, I can't find it anywhere except on digikey and mouser (which imply a cost of respectively €18 and €20 to Italy, whereas all the products amount to only €11-12...).

What can you tell btw regarding the resistors? Are those values correct, and what power rating should I choose?